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Re: 22 vac 0 boost... No leaks???

I don't know diddley about turbo setups, but if the engine runs fine, doesn't make any boost, and then makes a whoosh at around 3000 rpm.... I'd guess there is something opening up to create a BIG boost leak.

Drawing on my minimal knowledge of wastegates, I think that they are controlled with some kind of 3-way valve that the ECU uses to limit boost pressure by opening and closing the wastegate. Apparently the wastegate may have a spring with a low pressure rating that works as a kind of backup if the 3-way valve/servo controller craps out. This is based on reading "... the turbo was only operating at wastegate spring pressure".

These things appear to be sensitive to having the correct ports on the valve connected to the ports on the wastegate, so it would be worth checking if that noise you hear at 3000 rpm is not the wastegate opening prematurely. Depends a lot on what kind of electronic control you have on the wastegate, and there seem to be a lot of variations, but logic says the wastegate opening is one reason why you have no boost.

If you don't have a one way valve in the brake booster line, you will no (very little) brakes when the engine is not running.

Re: 22 vac 0 boost... No leaks???

Hey Jon

Thanks as ever for the reply and help dude.

That was one of my first thoughts. I checked the spring and it cracks at about 6 psi and fully opens by 8. No leaks on the bottom or top nipple (top nipple is vented/unused) or the fire ring (cleaned the seat) or housing (checked under water).

Sorry should of said I'm just running off the wastegate spring. Eliminated my boost controller cos I thought that was maybe my leak.

Brakes are "ok" but not mega sharp, I just put that down to running ebc yellow stuff pads (need warming up lol).

I'm baffled how I have 22 vac.

Rev it and the boost blows your hand off the dump valve t piece. Yet under load literally 0. Revved it and forgot to take off the turbo inlet cap and it literally sucked all the inlet couplers in from the vac.

Turbo fins etc/shaft/bearings all look/feel perfect.

Thinking now maybe the brake master cylinder seals itself under vacuum but leaks under boost? Possible?

Another wired one is sometimes it feels like the brakes are "on" as I pull away gently.

I've smoke and pressure tested the entire system and couldn't see/hear a thing. Next step I think is to get her out the garage again tmrw and fit another check valve to the brake booster hose.

Gonna make a cap for the exh v band and try to pressurise the entire system hot again. Will report back soon as I figure this last hurdle out lol.

Re: 22 vac 0 boost... No leaks???

I take it that you realisse that you probably wont get boost on the boost gauge to show unless the car is driven under load.
No matter how much you rev is stationary, most cars will never make enough boost to show on a gauge.

Re: 22 vac 0 boost... No leaks???

Hey man. Yeah was just revving it to see if it was pushing air (thought maybe the turbo shaft had gone or something just to cancel out it not making boost).

I used the boost gauge in the car while boost leak checking just to check it was the same as what the compressor was saying.

I'm almost certain it's actually making boost, just can't work out where it could lose SO much boost, pull so much vac, and not hear a sound. Thinking if the brake cylinder was passing it would whistle inside the car maybe why I hear nothing outside. Would have thought tho I'd hear it while driving?

Brakes work but are crap lol.

Thanks for the reply btw. Any help is greatly appreciated. After months of trouble shooting the brake booster is my last hope then I really am outta ideas. I'm guessing st205 brake boosters have an internal check valve. It's literally just a pipe to the intake manifold. Gonna add a one way valve to that bad boy tmrw n see if I can melt that paddle clutch : ) just wondering if a booster could leak pressure but still work "ok"?

Will try n take some videos tmrw in the car etc/on laptop while driving.

Another crazy thought is my Prehistoric LINK ecu has an internal map sensor (runs cleaner on this than the stock one). Maybe that leaks. Checked the coupler and it's super tight. It's also in the footwell so I'd Prob hear it. My cars pretty LOUD tho and all sound deadening a removed (am at 1090kg aiming for 1000kg it's pretty spartan for a daily) which doesn't help. It's gonna be something daft... I hope!

One last thought... The knock counts set to start at 2k on my ecu. Gonna set this to 4k tmrw n give it some loud pedal. The engines forged n pretty noisy. Could the knock sensor be going tits and pulling timing? Zero boost? Surely less timing would spool it up more???

Re: 22 vac 0 boost... No leaks???

My supercharged engine idles at 30 kPa (20.7" hg) and will go down to 20 kPa (23.6 "hg) on the overrun. The amount of vacuum that you have at idle is affected by the lobe separation angle between your inlet and exhaust camshafts. More lobe separation means less overlap and higher idle vacuum.

Turbo spool is affected by cam timing. According to what I read (and you can see that I have been doing a bit of reading)... More overlap => higher EGTs, slower turbo spool, more fuel, and Less overlap => lower EGTs, faster turbo spool, less fuel. Changing a stock cam for one with more duration will increase the overlap unless the lobe centres are adjusted. Ignition timing and exhaust gas temperature also have some affect on spool.

Which brings me to the point... you have an aftermarket ECU but you are setting the ignition timing to the OEM base timing for a 3S-GTE. On the factory ECU once you have calibrated the timing by jumping the diagnostic box and setting the base timing to 10 deg BTDC at idle, the ECU adds more timing when you remove the jumper wire. The FSM says you can expect the idle timing to fluctuate between 12 and 21 deg BTDC; so hovering around 16-17 deg BTDC.

But your Link does not operate like that. It will have an ignition map that says what timing it provides at idle rpm and all other rpm's. I would expect it to show something like 16-17 deg in the 900 rpm column and at something like 30 kPa. Calibration is usually done by locking the ECU timing at (say) 15 deg and using a timing light to adjust the distributor until the mark on the crank pulley reads 15 deg on the scale.

Of course, if your ignition map has idle timing of 10 deg, then you are spot on if you set the crank pulley to the 10 deg on the scale. But if you are 6 or 7 deg retarded, that can have a noticeable effect on a turbocharged engine. Just another thing to check while you are in there

Cheers... jondee86

PS: Yusss... if you granny it up to 4000 rpm you will not be applying much load. You don't need to beat on it but you should be making sure it is getting some reasonable load running up and down thru the gears. Use 3rd and 4th if you can

Re: 22 vac 0 boost... No leaks???

Hey Jon/all

You have no idea how much I appreciate your help dude/s every time I come on here cos I'm stuck.

Your absolutely right.

I put the stock 240/236 cams back in and used adj cam pulleys to get them both zero'd to eliminate the cams (only mild hks 256s) Checked the no 1 pot was at tdc with a screwdriver and the mark was also spot on on the crank at 0. I locked the timing on my LINK to 0 and set the idle to a steady 10 btdc.

I'm pulling between 30 and 35 kpa at idle too. Closed loop set to around 13.9 at idle. Timings about 16-17 your spot on! It seems to like more timing at idle...

Trying to bribe my GF into videoing my laptop to see if it's pulling timing but it's FREEZING in the uk and she says my cars to cold and loud to help me lol.

Boys at work/friends all drive 1 litre hamster powered shiny Eco hair dryers and just don't get it lol. I'm the only engine addict I know. This is why I LOVE Toymods It's like therapy : )

Dude would a shafted knock sensor pull enough timing to not make boost? Not heard any pinging or det. I've got a knock alert and meth injection just incase... (disconnected tho to eliminate the nozzle/piping as a leak).

In 1st to 3rd even with no turbo it still pulls ok just very slowly. I'm aiming 14 afr is at idle, 13 ish 1000 - 3000rpm/50-100kpa spooling up). Aiming for 10.5 - 11 afr soon as I actually make full boost lol. Plan to pull 2 degrees from all over the base map. Get the fuel curve right first. Edge the timing back and slowly up the boost from 8psi to 22... Soon as I nail this last hurdle and run it in It SHOULD go like a raped ape on crack...

With a GT2860rs on stock cams I should be battling boost creep and full boost by 3k not 1psi. Man I'd give my left nut to find this ghost leak.

Might advance both cams say 3 degrees for more low end and see what happens too. I'm sure it's a boost leak tho and not the base map. I'm slowly trying to road map alone cos there's no 4wd dyno anywhere near Hull I know of. I've contacted the only local tuner I know of here n here's scratching his head too.

Re: 22 vac 0 boost... No leaks???

Hey Oldcorollas,

Gt2860rs is slightly bigger than a stock ct20b. Slightly. There known as "disco potatoes" on nissans and on a 3sgte should be at full boost by 3k. Spools supposed to be v fast (full ball bearing) people run them on sr20det's religously.

Stock st205 ct20b's can make 330bhp so it's in the right ballpark. I'm still on stock 550 injectors. All should be good...

My LINK ecu came off a stock ish st205 mapped for a turbo technics s148 (hybrid ct26) apparently which is rated again 340 - 400bhp and from what I've read v similar to a gt2860rs in spool and power.

I've dropped the master fuel by 13 % and got the beast to run 13 ish afrs idle to spool around 3k. Was mega rich at first.

Timings conservative till I dial everything else in. Using lots of octane booster just in case and a innovate lm wide band. Should make boost without any issues.

I'm thinking knock sensor/brake booster leak... Around 3k it whooshes/whistles like it's making but not holding boost. It makes absolutely no sense cos there's no where left to test???

Wish I'd dropped a rag in one of the charge coolers dude. Had em off. All clear unfortunatly.

Appreciate the reply/help/ideas btw dude. It's ridiculous to think someone could find my fault without even seeing the car but all the ideas are helping me... I musta overlooked SOMETHING...

Btw if I'm wrong about the gt2860rs being a stockish upgrade on a rev 2/3 3sgte someone pls put me straight, cos I'm no turbo expert just going on tried n tested recommendations etc. it's driving me nuts now lol. Cycling to work at 4am in the bitter frost sucks. I'm either buying a new turbo this month or some extra warm long johns and Valium cos I'm close to burning my car. Actually for real started thinking ex wife's voodoo cursed my car : )... seriously...

Re: 22 vac 0 boost... No leaks???

Originally Posted by Blackcountryboy

I locked the timing on my LINK to 0 and set the idle to a steady 10 btdc.

Sorry dude, but if this is what you actually did, I'd say you did it wrong. Whatever you lock the timing at is the timing you have to set with your light. This calibrates the timing delivered by the ECU to the crank position. So if you lock it at (say) 10 deg BTDC (zero is a bit low for decent idle) you need to set the crank pulley to 10 deg BTDC on the scale with your light by adjusting the distributor.

If I am reading the situation correctly, you built in 10 deg of advance that the ECU knows nothing about. When the ECU is unlocked it returns to delivering the advance set in the ignition map. Therefore if the laptop is showing you idling at 16-17 deg at idle, you will actually be getting spark deliverd at 26-27 deg BTDC.

You can check the actual timing by warming the engine up and putting the light on the crank pulley. I don't mind being wrong about this as I'm not an expert on Link or anything... but worth checking.

Re: 22 vac 0 boost... No leaks???

Originally Posted by jondee86

Sorry dude, but if this is what you actually did, I'd say you did it wrong. Whatever you lock the timing at is the timing you have to set with your light. This calibrates the timing delivered by the ECU to the crank position. So if you lock it at (say) 10 deg BTDC (zero is a bit low for decent idle) you need to set the crank pulley to 10 deg BTDC on the scale with your light by adjusting the distributor.

Cheers... jondee86

Depends on the link. If it is truly old and is a G1 ECU,
they are usually set like that at 10 deg with the advance zero'd
as when cranking there is no ECU timing at cranking speed and to get it to start you set them at 10,
and tune accordingly.
If you set it at 0 it wire fire at TDC while cranking which does not help starting.

That was the best part of the upgrade to later ecu's is that the timing map showed actual timing.

Re: 22 vac 0 boost... No leaks???

Fair enough... I never used an old Link so just thought that all ECU's would calibrate using the same basic technique. So if the timing light is showing 16-17 deg at idle, scratch everything I said above

Re: 22 vac 0 boost... No leaks???

Hey all,

Really good point Jon. Im hoping ive set the timing right. Hoping it might be that simple. Its a LINK G1 PLUS. The manual just said to set the advance to 0 in the configuration menu , then rotate the dizzy to the 10 degree mark on the crank, tighten it down then put the advance back to 40 on the ecu.

Im gonna re read the manual tonight on me nightshift to double check. You might be right and ive messed up the timing. Seems to run ok tho. Gonna do some videos today so you can actually hear/see what the laptop/guages are doing.

Re: 22 vac 0 boost... No leaks???

Went back to garage the other side of town and tried to make a few videos for you guys.

Soon as i got her warmed up and went for a spin my effing phone died.... ARRRRRGH.

Gonna go back tmrw afternoon soon as im awake after my shift and try taping my phone to my roll cage so i can give you an idea off whats what under load.

So... i fitted a check valve on the brake booster.... Took the knock start count upto 4k on the LINK. No change unfortunatly. 2k to 3k in 2cnd/3rd even put her in 4 and laboured the endine to try n get something... boost guage just goes to zero and barely holds one psi regardless of revs or load. Piston rings??? one sixty psi on every cylinder tho and 22 vac. Makes no sense...

Soon as i got back i put a rag in where the idle hose goes into the boost line. Blipped the throttle and it literally blew the rag at the windscreen like a bullet. Its making SHED LOADS of boost.

Theres a bit of blowby coming out the oil cap/pcv but nothing major considering its done less than 20 miles so far.

Re: 22 vac 0 boost... No leaks???

Kind of difficult for me to read the numbers on your laptop but from what I can see the numbers look to be normal. If the tune came from another car then you could expect the AFR's to be a bit out for your engine. Getting that sorted is part of the tuning process. I'm not going to advise changing the whole fuel map but you can't do any damage by changing a few cells around idle.

Make a note of which cells you change and by how much, so that you can change them back if the engine starts to hunt (surge) at idle. Then, when the engine is warmed up you can take a few percentage points (say 5%) out of the idle cell and see how the AFR changes. Around 14:1 seems to work for most engines... still a bit on the rich side but OK.

Not sure how your ISCV is set up, but I guess one side is open to atmosphere and the other side is connected into an intake tube that sees boost. That means that the ISCV should be shut when boosting to avoid being a boost leak. Just a little thing but worth checking.

I don't have a turbo and haven't worked with a lot of different ECU's. So I just make suggestions based on my own experience with my s/c engine and ECU, and what makes sense from a logical point of view. It is always nice to be able to make a sanity check, and in the case of the ignition timing, you can do that with your timing light.

Given its history, I don't think that there will be any benefit in babying your engine now. If it were mine I would try and get it on a suitable deserted piece of road and give it a series of runs thru the gears with increased throttle and increased rpm on each run. Depending on how the engine performs and what your gauges tell you, this might take a dozen runs with a cool down after six runs.

By the end you should be hitting 7000 rpm in 3rd if that is a safe speed on your piece of road. The actual speed is not important... what you need to be doing is gradually icreasing the load on the engine and the rpm's until you are using full throttle. If the engine has not blown up it is now fully run in. Change the oil and drive it normally.

If you cannot find a simple mechanical reason for lack of boost (clogged catalyst, cam timing, boost leak etc) then it might be that that the engine is just not doing enough work when you have been road testing. The turbine needs gas flow and heat for spool. Gas flow is largely controlled by the throttle position and heat is the byproduct of the engine doing work. So basically you need to put load on the engine to get some heat out of the combustion chambers and into the exhaust.

With a turbo there are a number of factors that affect this process. Fueling, ignition timing, cam timing and turbo sizing all influence how soon and how hard the turbo spools. I don't know if any one or combination of these factors could cause the problem you have. Seems unlikely, but I'll just ask you about anything I think might be worth checking